1. Mechanical Engineering Department, Amirkabir University of Technology, Tehran, Iran
2. Department of Physics, Amirkabir University of Technology, Tehran, Iran
3. University of South Florida, Department of Mathematics and Statistics, Tampa, FL 33620-5700 USA / Department of Mathematics, Science Faculty, Ege University, 35100 Bornova-Izmir, Turkey
4. Civil Engineering Department, Amirkabir University of Technology, Tehran, Iran